近岸典型养殖海区潮流垂直结构的数值研究

Modeling studies on vertical structure of tidal current in a typically coastal raft-culture area

采用改进的一维水动力模型对我国近岸典型筏式养殖海区的潮流垂直结构进行了数值研究。模型通过增加潮流上边界层来描述养殖活动与潮流垂直分布的关系。数值实验结果表明,高密度养殖对潮流的阻碍作用很强,使得海水表层流速显著减缓;当养殖密度达到临界值后,流速剖面出现变形,流速迅速减小。流速剖面随底应力的变化也会出现同样的变形。潮流流速及其垂直分布情况均受到上层养殖阻力和海底应力的共同作用,呈非线性变化趋势。潮流垂直结构就是对在外海传入潮波的驱动下,海水对上层养殖阻力和海底应力的适应与调整。这为进一步优化养殖设施布放、养殖品种安排等奠定了理论基础。生物生长与吊笼等因素对海水运动的阻力效应是需要进一步考虑的问题。

Vertical structure of tidal current in a typically coastal raft-culture area is discussed by a numerical model. A one-dimensional hydrodynamic model was modified to include the tidal surface boundary layer for describing the interaction between aquaculture and tidal flow and parameterized with the field data. It replicated the observed velocity profile and was then used to investigate the impacts of varying culture densities and bottom frictions on the vertical tidal current structure. Modeling results indicate that the surface current velocity was largely damped because culture activities enhanced the frictional effects on flow intensively. The magnitude and vertical structure of tidal current are determined by aquaculture drag and bottom friction. The magnitude damps so rapidly that the vertical double-log profile is distorted within a water column when the frictional effect of culture density increases to a certain threshold value. The vertical structure is remarkably deformed by the varying magnitude of bottom friction. In addition,the vertical velocity structure has a nonlinear trend along with culture density and bottom friction. The variation of the vertical structure is a kind of adaptation/adjustment to both surface friction （aquaculture drag） and bottom shear stress under the tidal forcing. This study is a theoretical foundation for optimizing aquaculture configuration through regulating culture density and species distribution. The frictional effect of culture-organisms-growth and suspended cage on the flow should be considered in further studies.